There has been a long-felt need for methods of directly influencing hair growth, color and appearance, especially for treatment of alopecia in humans.
Surgical transplantation of small, discrete, skin areas having viable follicles to areas having inactive follicles is expensive, labor-intensive and relatively short-lasting. Also, as described by R. F. Oliver et al. in U.S. Pat. No. 4,919,664, follicular dermal cells can be inserted into a skin incision, resulting in hair growth along the incision. However, this is a complex technique that does nothing to stimulate existing follicles.
Treatment of the hair and skin with various creams or lotions with biologically active ingredients to improve hair growth and other conditions has generally low efficiency. A wide variety of externally applied agents are available for application to the hair to improve body, flexibility, curl, etc. These have limited and only short term usefulness. Coloring hair with various dyes requires frequent repetitions and is not always natural in appearance.
The use of biologically active compounds that are hair growth stimulators or advantageously change other hair characteristics, such as color, would seem to be a more natural and attractive approach, especially at the stage where hair-follicle cells still exist but hair growth, for unknown reasons, is adversely affected. Attempts to follow this approach have been ineffective, possibly because of the inability of stimulators to penetrate the cellular membrane of hair follicle cells and to enter into the cells where their action is needed.
In the treatment of skin with various absorbable lotions and the like it has long been known that absorption is generally greater in skin areas of higher follicular density. See, for example, Maigach et al, Arch. Environ. Health, 23:208-211 (1971). The absorbed materials, however, were entirely different from liposomes. It was not appreciated prior to the present invention that liposomes could be used to direct beneficial compositions preferentially to hair follicles.
Liposomes, which are artificial phospholipid vesicles, have been successfully used for delivery of different low-molecular-weight water-soluble and oil-soluble compounds into different cells. See, for example, G. Gregoriadis, Trends in Biotechnology, 3:235-241 (1985) and K. H. Schmidt, ed., Liposomes as drug carriers, Stuttgart: George Thieme Verlag (1986).
Liposomes are typically formed by mixing dry phospholipids with aqueous solutions giving rise to bilayers of phospholipid molecules which arrange themselves spontaneously to form close multilayered spherules. As they form, the liposomes entrap liquid and any soluble solutes that are present. A large number of substances that do not interfere with the formation of the liposomes can be incorporated, regardless of solubility, electrical charge, size and other structural characteristics. These characteristics may, however, have adverse affects in some environments limiting the use of liposomes.
Liposomes containing antibody molecules attached for specific targeting have been described for delivery of encapsulated material to targeted cells containing an antigen immunoreactive with the attached antibody, and are referred to as immunoliposomes. See, for example, U.S. Pat. Nos. 4,755,388, 4,925,661 and 4,957,735 for descriptions of immunoliposomes. In addition, liposome compositions have been described that contain protein which are administered to mammalian skin and shown to penetrate in skin keratinocytes. See, U.S. Pat. No. 5,190,762. Furthermore, DNA-liposome compositions have also been described, but were not shown to selectively deliver the nucleic acid contents to hair follicles through topical administration. See, U.S. Pat. Nos. 5,077,211 and 5,223,263, and Hoffman et al., FEBS Letts., 93:365-368 (1978).
Although various targeting mechanisms have been attempted to increase the specificity of delivery via liposomes, delivery of the encapsulated material into a targeted cell or tissue may not necessarily follow.
Specific tissue delivery is particularly important where the agent being delivered may have a deleterious effect to tissues adjacent to the targeted tissue of interest upon administration of the agent. For example, the agent may produce effects which are acceptable in the hair follicle, but not desired in the adjacent skin tissue. For example, delivery of melanin is desirable for hair pigmentation, but may or may not be desirable for general skin pigmentation, and therefore general delivery to all surface skin cells may be undesirable, requiring follicle cell specificity. Similarly, gene replacement therapy for expressing melanin or tyrosinase may be undesirable in skin cells, but is a desirable result for hair pigmentation.
Transdermal drug delivery provides additional problems where the drug being delivered is destined for the circulation rather than cells of the dermis. Methods for transdermal drug delivery which minimize adsorption into cells of the skin and simultaneously increase transport to the circulation are desirable in certain instances. However, in instances where delivery is directed solely to the hair follicle, it is desirable that there is minimum adsorption into the skin and minimum transport of the compound into the systemic circulation where the administered compound can exert undesirable side effects.
A small molecule dye, carboxyfluorescein has been found to be delivered to the pilosebaceous units of hamster ear membrane when incorporated in a particular liposomal formulation, as described in a very recent paper by Lieb et al, The Journal of Investigative Dermatology, 99:108-113 (1992). Similarly, Li et al., In Vitro Cell. Dev. Biol., 28A:679-681 (1992), have recently described liposome-mediated delivery of the small molecule dye calcein to hair follicles in an in vitro intact skin histoculture system.
The prior research, however, does not describe methods of specifically and selectively (preferentially) targeting hair follicles using liposomes containing large molecule agents such as proteins or nucleic acids, lipophobic agents that cannot transfer across lipid barriers or lipophilic agents which are capable of undesirable side effects on tissues other that hair follicles.
Furthermore, there have not been any descriptions of methods for accurately testing in vitro the extent to which particular compounds are delivered to hair follicle cells, the effectiveness of the compounds delivered, or liposome formulations for optimizing selectivity of targeting to hair follicles.
Thus, there is a continuing need for improved methods of selectively delivering specific beneficial compounds to hair follicles, and for measuring effectiveness of the delivery.